A robust and reproducible scapular coordinate system is necessary to study scapulothoracic kinematics. The coordinate system recommended by the ISB (International Society of Biomechanics) is difficult to apply in studies using medical imaging, which mostly use a glenoid-centered coordinate system. The aim of this study was to assess the robustness of a glenoid-centered coordinate system compared with the ISB coordinate system, and to study the reproducibility of this coordinate system measure during abduction. A Monte-Carlo analysis was performed to test the robustness of the two coordinate systems. This method enabled the variability of the orientation of the coordinate system to be assessed in a laboratory setting. A reproducibility study of the glenoid-centered coordinate system in the thorax reference frame was performed during abduction in the scapular plane using a low-dose stereoradiography system. We showed that the glenoid-centered coordinate system was slightly more robust than the ISB-recommended coordinate system. Most reproducible rotation was upward/downward rotation (x axis) and most reproducible translation was along the Y axis (superior-inferior translation). In conclusion, the glenoid-centered coordinate system can be used with confidence for scapular kinematics analysis. The uncertainty of the measures derived from our technique is acceptable compared with that reported in the literature. Functional quantitative analysis of the scapulothoracic joint is possible with this method.
Xavier Ohl, Pierre-Yves Lagacé, Fabien Billuart, Olivier Gagey, and Wafa Skalli are with Laboratoire de Biomécanique, Arts et Métiers ParisTech, Paris, France. Xavier Ohl is also with CHU Reims, Service d’Orthopédie-Traumatologie, Reims, France. Pierre-Yves Lagacé and Nicola Hagemeister are with Laboratoire de recherche en Imagerie et Orthopédie—École de technologie supérieure, Centre de recherche du Centre hospitalier de l’Université de Montréal, Montréal, Canada. Olivier Gagey is also with Service de Chirurgie Orthopédique, CHU de Bicêtre, Université Paris, Le Kremlin-Bicêtre, France.